1. Field of the Invention (Technical Field)
The invention relates to testing apparatus for heavy metals, more particularly disposable, printed electrodes; and a method of using such apparatus.
2. Background Art
Anodic stripping voltammetry (ASV) and potentiometric stripping analysis (PSA) have long been used in trace metal testing, as discussed in "Anodic Stripping Voltammetry as an Analytical Tool" (by Wang Environ. Sci. Technol., Vol 16, No. 2 (1982)) and "Mercury-Coated Carbon-Foam Composite Electrodes for Stripping Analysis of Trace Metals" (by Wang, et al., Analytical Chemistry, Vol. 64, (1992). Anodic stripping voltammetry generally involves the reduction or electrolytic deposition of metals onto an electrode, termed preconcentration, followed by anodically reoxidizing and stripping the metals, thereby producing a plot of current as a function of voltage increasing in amplitude (the measurement step), as discussed in "Anodic Stripping Voltammetry" (by Wang Journal of Chemical Education, Vol. 60, P. 1074).
Normally, ASV and PSA require laboratory conditions for optimum results (see Wang, "Anodic Stripping Voltammetry"). Beakers, nitrogen bubbling equipment, and stirrers are usually required. Electrodes for ASV comprise a working electrode, reference electrode (usually Ag/AgCl), and an auxiliary electrode, usually platinum.
Prior art working electrodes for ASV and PSA, such as those in U.S. Pat. No. 4,804,443, entitled Method and Apparatus for the Determination of Electrochemically Active Components in a Process Stream, to Newman, et al., comprised hanging mercury drop and mercury-coated glassy carbon electrodes. The hanging mercury drop electrode requires laboratory conditions to insure stability and drop size of the drop. As discussed in "Mercury-Coated Carbon-Foam Composite Electrodes for Stripping Analysis of Trace Metals," by Wang, et al., (Analytical Chemistry, Vol 64 (1992)) glassy carbon substrate electrodes also give better results under laboratory conditions.
Two articles entitled "Disposable Single-Use Sensors" and "Disposable Electrochemical Biosensors" (by Monika J. Green and Paul I. Hilditch, MediSense Inc., Units 3 and 4) discuss single-use disposable sensors, also well-known to the prior art. Biosensors, for example, glucose monitors, may comprise a PVC substrate with a working (carbon) and reference (Ag/AgCl) electrodes coated thereon, as well as the enzyme. Such enzyme-coated electrodes are also described in parent application Ser. No. 07/682,907, incorporated herein by reference. Other prior art applications of screen-printed electrodes are electrochemical measurements of ascorbic acid or reduced glutathione.
As disclosed in the parent application, working electrodes, particularly flat or planar carbon paste electrodes, can effectively be modified. Chemical and biological modification involving selective electrode coatings or membranes, are disclosed. Also disclosed in the parent application is the use of optical or thermal devices as sensors.
Parent application Ser. No. 07/682,907, while generally disclosing apparatus and method for batch injection analysis, also used voltammetric and potentiometric measurements and measurement devices therein.
A requirement for decentralized testing of trace metals has evolved. Field or on-site trace metal testing further suggests a need for disposable single-use electrodes. However, despite the ready availability, low cost, and general convenience of screen-printed carbon electrodes, formerly used primarily as biosensors, they are nowhere in the prior art suggested for use in trace metal detection apparatus.